Optical waveguide fibers are normally provided with a plastic protective coating applied by the fiber manufacturer directly over the cladding to protect the fiber.
In tight buffered cables, a protective tube is applied by the cable manufacturer directly to the outer surface of the fiber coating so that the fiber and the tube are in contact substantially along their lengths. In loose tube or composite buffer constructions, the coated optical fiber is separated from the protective tube.
U.S. Pat. No. 5,627,932 relates to a single optical waveguide fiber having an outer coating, a layer of loose tensile fibers surrounding the optical waveguide fiber outer coating, and a tubular jacket of plastic material surrounding the layer of loose tensile fibers. The cable contains no gel-like compounds. The layer of loose tensile strength fibers, such as Kevlar aramid fibers, is twisted around the buffered optical fibers, and an outer jacket of plastic material is extruded around the layer of said strength fibers.
U.S. Pat. No. 7,035,511 relates to a protective casing for an optical waveguide fiber including an outer tubing, an inner tubing with a passageway therethrough, and a layer of strength members. The outer tubing is preferably PVC, and the materials for the inner tubing can include suitable grades of polyetherimide, polyetheretherketone, or fluoroplastic THV. The layer of strength members is positioned between the outer tubing and the inner tubing for carrying any applied tensile load, and these strength members are aramid fibers or fiberglass fibers that allow flexibility while providing the necessary tensile strength. The layer of strengthening members includes a plurality of strands of aramid yarn that are wrapped about the outer surface of the inner tubing during manufacture. The protective casing is thus made of three separate materials (i.e., the polyetherimide inner tubing, the aramid strength fibers, and the PVC outer tubing).
U.S. Pat. No. 6,091,871 relates to a reinforced optical fiber cable comprising a protective tube for protecting optical fibers, a reinforcing layer and reinforcing rods around the protective tube, together with an outer sheath. To protect the optical fibers against penetration of moisture, the inside space holding the optical fibers contains a filler material. The cable of the ′871 patent further includes strengthening rods embedded in the sheath positioned parallel to the cable axis and a reinforcing layer that is between the protective tube and the outer sheath. The reinforcing layer may include wires or elements having high traction strength, i.e., fibers made of aramid, glass, or fiber reinforced plastic (FRP) material, which are wound helically around the tubular structure.
European Patent Application No. 0 005 029 relates to an optical fiber unit consisting of a tubular sheath surrounding optical fibers. The sheath is reinforced by two steel wires, which are embedded in the tube wall, diametrically opposite to one another, and which extend continuously along the whole length of the sheath. The sheath is made of polyethylene.
U.S. Pat. No. 5,627,932 relates to a tight buffered optical fiber cable containing optical fiber surrounded by a coating applied directly over the optical fiber. A layer of loose tensile strength members is applied over the buffered optical fiber, and an outer polymer tubular jacket is extruded over the aforementioned layer, wherein the outer jacket is formed of PVC material.
One disadvantage of the optical fiber cables according to the prior art is that the tight buffered fibers and the central filled loose tubes are expensive. Moreover, accessing the fibers is a time consuming process, and especially when a gel-filled, central loose tube is used, fiber cleaning is necessary.